FIRE RETARDANT MECHANISMS RELATING TO SMOKE AND TOXIC PRODUCT YIELD FORM EVA COMPOSITES

摘要

A Purser furnace has been used to investigate the combustion toxicity of ethylene-vinyl acetate copolymer (EVA) with and without fire retardants, under different fire conditions. Steady state flaming combustion has been studied at equivalence ratios φ varying from 0.5 to 1.5 by driving the materials through the furnace at 750℃. Yields of CO for EVA containing around 27% vinyl acetate, and its fire retarded composites, containing fire retardant fillers are presented. The materials contained aluminium hydroxide (ATH) or magnesium hydroxide (MH), with zinc hydroxystannate (ZHS), magnesium borate (MB), zinc borate (ZB) or an organoclay. In each case the same mass of EVA was used in the determination. The yields of CO per g of polymer from the EVA-fire retardant composite samples showed very similar yields of CO under well ventilated conditions to the pure EVA, but generally higher CO yields than the base polymer under the most toxic fuel rich conditions. The exception to this was the sample containing ATH and zinc borate, which did not take up all the available oxygen under fuel rich conditions, and gave a much lower CO yield, corresponding to an eight-fold reduction in the combustion toxicity. Where the samples were also tested in the cone calorimeter, CO yield and smoke levels are reported comparatively. In order to understand the fire behaviour, mechanistic studies have been undertaken using thermal analysis.